Punisher is the recipient of multidisciplinary military training from the U.S. Marine Corps. While a Marine, he also received training from the U.S. Army and Navy. From this training, Punisher is proficient in not only basic infantry skills, but in special operations, which includes the use and maintenance of specialized firearms and explosive ordnance. He is highly trained in infiltration into heavily-guarded enemy territories and structures for the purpose of assassination, captures, and military intelligence. Also, he is trained in various forms of camouflage and stealth. From his airborne training, Punisher is able to pack and maintain his own parachute rigs, as well as professionally control his landings, in daylight and at night. From his Navy UDT training, Punisher is well-skilled in extended underwater operations, including demolitions. He is skilled with a great many types of explosives, ranging from simple dynamite to plastique to improvised explosives. His hand-to-hand combat skills are more then sufficient to allow him to incapacitate and kill men much stronger than he is, as well as to deal with groups of armed and unarmed enemies, killing them all without weapons if he deems it necessary. He is also extremely deadly in knife training, preferring the knife he learned to fight with in the USMC: the ka-bar. Additionally, he is a preternaturally-precise marksman. He is thoroughly trained and experienced in unconventional ("guerilla") warfare. He is an armorer, a gunsmith, and an expert in field medicine.

Born in New York to parents of Italian ancestry, Francis Castiglione is a former U.S. Marine Captain. Before Frank joined the Marines, he was studying to become a Catholic priest but changed his mind because he was unable to forgive those who did evil. Also prior to his enlistment, he married his wife Maria who was already pregnant with their first child. During his time in the United States Marine Corps (USMC), Castle graduated from Basic Training, then went on to Infantry School. Immediately following that, he went through the USMC's Reconnaissance, Force Reconnaissance, and Sniper Schools. Attaining dockets, Castle was permitted to go through U.S. Army Airborne School, and U.S. Navy Underwater Demolition Team training, becoming qualified as a Navy Seal (Sea, Air and Land). He served in the Vietnam War in a special forces unit as a point man. For heroism in the line of duty, he was decorated with numerous medals, including the Purple Heart.

Shortly after a tour in Vietnam, Castle, his wife, Maria and their children were in New York's Central Park for an afternoon picnic when they witnessed a Mafia gangland execution; an informant had been hanged from a tree. Seeking to eliminate all witnesses, the Costa crime family murdered them on the spot. However, Castle survived.
Even though Frank was able to identify all of the shooters the police were unable to help Castle in his quest for justice; they were tied in too deeply to the powerful Costa family. He decided that the only punishment criminals might receive is that of physical destruction. Shortly thereafter, he emblazoned his body armor with a symbol of a death's head, and exacted his revenge. Since then he has waged a one-man war upon crime, taking the name Punisher.

In his vigilante endeavors, Castle has crossed paths with several costumed crime-fighters, most notably Spider-Man and Daredevil. These encounters have often resulted in his incarceration. While he is known to be significantly inferior to Daredevil in hand-to-hand combat skills, Punisher has been rated as one of the most dangerous criminals alive. When he was incarcerated in New York's Riker's Island Prison, though heavily outnumbered in gang-fights, Punisher has routinely killed armed, homicidal criminals with frightening ease, sustaining no injury. Due to his proficiency in fighting, he is rarely so accosted in prison environments. Adhering to his military philosophies, Punisher is constantly training whenever he is not out on actual maneuvers. He exercises fanatically to maintain his impressive physical conditioning and sticks to a balanced diet whenever possible.